WASHINGTON — As President Obama’s national security team considers military options for assisting Iraq against advancing Islamist extremist militants, one key worry for the US is this: What happens if the sophisticated US arms the Iraqi government seeks fall into the hands of the anti-US militants?

It’s the same question that has kept the US from sending arms to the moderate opposition in the civil war in neighboring Syria, where the militants of the Islamic State of Iraq and the Levant (ISIS), now holding major cities in Iraq and moving toward the outskirts of Baghdad, also control territory in the north.

Faced with video images from this week’s events in northern Iraq of US-trained-and–equipped Iraqi forces abandoning their weapons, ammunition, and armored vehicles before the advancing militants, US officials will be considering the wisdom of sending more missiles, helicopters, and other weapons to a military that might just give them up.

Mr. Obama gave a statement from the White House south lawn Friday afternoon in which he suggested that it will still be several days before he decides what steps the US will take to bolster the government of Iraqi Prime Minister Nouri al-Maliki in its fight with ISIS.

But the president used his statement to signal to Mr. Maliki that any US assistance in Iraq’s grave hour will be contingent upon the government of Iraq taking meaningful steps toward political unity and sectarian reconciliation.

“Any action we may take to provide assistance to Iraq’s security forces has to be joined by a serious and sincere effort by Iraq’s leaders to set aside sectarian differences, to provide stability and to account for the legitimate interests of all of Iraq’s communities,” the president said.

In effect, Obama is using Maliki’s moment of weakness and extremity as leverage to get the Shiite leader to undertake the kinds of political actions and reaching out to the country’s alienated Sunni minority that the US has been encouraging for years.

Calling the week’s stunning exposure of Iraq’s sectarian and geographical fissures “a wake-up call” to the government, the president said that “in the absence of this type of political effort, short-term military action, including any assistance we might provide, won’t succeed.”

The US has already provided Iraq with well over $10 billion in military equipment, ranging from ammunition to missiles and helicopters, with another $1 billion currently in the pipeline, according to Defense Department officials.

Under pressure of militant advances – signs of which have been mounting in recent months, with an acceleration in car bombings and other violence that last month left more than 700 Iraqis dead – the Maliki government has also been pressing for a speedup in the delivery of F-16s and Apache helicopters it is purchasing from US defense contractors.

Some Iraq experts are recommending caution on the question of sending more arms into Iraq. Hillary Mann Leverett, who served on President George W. Bush’s national security team before resigning in 2003 over disagreements with the administration’s Iraq policy, says deeper US involvement in the regional conflict will only serve the Islamists’ purposes.

“Contrary to conventional wisdom, the core problem in Iraq is not its prime minister’s flawed governance, but a decision by the US and its regional ‘allies’ to arm, fund, and train Sunni militias, first in Iraq as part of the ‘surge’ and then, indirectly, in Syria as part of a strategy to check Iran’s rise in the region,” says Ms. Leverett, now a professor at American University’s School of International Service in Washington.

“In this context,” she adds, “for the US to send more arms – to either the Iraqi government or indirectly to ISIS through so-called ‘moderate’ Syrian oppositionists – or itself to become more engaged in the conflict will only feed into the grand strategies of ISIS and Al Qaeda.”

One action the Maliki government is seeking – and one that circumvents the issue of US arms falling into the hands of Islamist extremists – is American airstrikes against the ISIS fighters. The US appears to be preparing for a presidential decision to go this route, with Pentagon officials saying Friday that an aircraft carrier, the USS George H. W. Bush, would soon arrive in the northern Gulf.

Some members of Congress wasted no time in blasting Obama’s statement in which he said he would be making a decision on action over the next several days, demanding immediate air strikes instead. “We need to be hitting these columns of terrorists marching on Baghdad with drones NOW,” the chairman of the House Foreign Affairs Committee, Rep. Ed Royce (R) of California, said in a statement.

Another Republican, House Armed Services Committee Chairman Buck McKeon of California, said he fears the president – whom he said is good at “considering options” – will in the end decide not to take action, “as he did in Syria” when he decided against striking the forces of President Bashar al-Assad over the use of chemical weapons.

But the US, in effect, becoming the air force of Iraq, even if only temporarily, is not without potential complications, defense analysts say.

One problem is that the insurgents don’t always move in easily identified columns but move around among civilians and take up positions among civilian populations, analysts note. This means the US could end up firing on and killing civilians – and find itself embroiled in the kind of anti-US controversies that have accompanied US drone strikes in Pakistan and Yemen.

If manned aircraft is used to attack the well-armed extremists, that raises the prospect of US bombers being fired on or shot down – and even of American pilots being captured. The ISIS militants have used gruesome videos of beheadings of captured enemies as part of a psychological campaign to deter and deflate opposing forces. A war-weary and largely anti-interventionist US public might shift quickly at the sight of a US pilot being paraded by militants, or worse.

A return to US military action in Iraq also raises the prospect of the US fighting in a war on the same side as Iran, which is the closest ally of the Shiite Maliki. With reports surfacing Friday of units of the Iranian Revolutionary Guard Corps already in Iraq to help protect the country’s revered Shiite shrines, the surreal picture begins to form of American fighter jets providing air cover for not just the Iraqis, but the IRGC.